Contained herein is material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction of the patent disclosure by any person as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all rights to the copyright whatsoever.
1. Field of the Invention
The present invention is related to the field of thermal management. In particular, the present invention is related to a method and apparatus for measuring cooling efficacy of a fluid medium.
2. Description of the Related Art
Power supplied to electronic equipment produces heat. Too much heat causes electronic components to deteriorate and eventually fail. Hence, some means of cooling the electronic components is necessary. Many methods and devices are employed to cool electronic components. Movement of a fluid medium, such as air, over the electronic components is one of the most common methods. Heat sinks, fans, heat exchangers, and coolant pumps are some of the most commonly used devices for facilitating the removal of heat. In a system that uses air as the cooling fluid, heat from an electronic component is transferred to the air surrounding the component. The heated air is moved away from the electronic component and is replaced by fresh air, resulting in the cooling of the electronic component.
The cooling efficacy of a fluid is a measure of how well a fluid cools a particular mass. The efficacy of a fluid depends on several parameters. The most significant of these parameters are the temperature of the fluid (air), and the quantity of the air moved over the mass. The temperature of the air commonly depends on the ambient environment. The quantity of air moved is controlled by any of several devices. Typically, these devices are fans and blowers. Thus, the quantity of air moved depends upon how fast a fan turns.
The quantity of air moved by a fan or blower also depends on the density of the air. At lower altitudes air is more dense, and therefore for a given fan speed more air is moved at lower altitudes that at higher altitudes. This means that the cooling efficacy of air depends, in part, on altitude. The simplest solution to guarantee sufficient cooling of electronic components under any conditions is to move enough air by simply running the fans at full speed. However, this mode is not efficient since more cooling effort is expended than is necessary. Also, moving air generates acoustic noise. Acoustic noise generation is undesirable especially when generated by a fan in a projector such as a movie-projector or a data-projector.
In some instances when a fan is used to cool heat sensitive electronic elements, such as to cool a lamp in a projector, using a fan controlled by a temperature sensor mounted on a circuit board is not the optimum solution. The fan speed, when controlled by a temperature sensor mounted on a circuit board, could be variable. This means that for various modes of operation, as different components on the circuit board are turned on, the variation in heat generated causes the fan speed to fluctuate. This variation in fan speed is undesirable, as a high-speed fan with continually changing speeds may generate disagreeable noise. Moreover, in the situation described above, the speed of the fan changes in response to the heat generated by components on the circuit board rather than in response to the changes in cooling efficacy of the air.
A heat sensitive element such as a lamp in a movie or data projector may be located some distance away from the circuit board. In other instances, due to the variability in the design of the circuit boards for different models of the same product, the location of the temperature sensor on the circuit board may be at varying distances away from the heat sensitive element. This variability complicates engineering predictions and increases development time.
Moreover, since air density changes with altitude, any product used to cool electronics at random altitudes most cope with this variability. This means that a cooling system that uses a temperature transducer on a circuit board for its input may not operate efficiently enough in order to cool a heat sensitive element operating at random altitudes. What is needed, therefore, is a method and apparatus to directly measure the cooling efficacy of air.